Spatial structure of b-substituted alkoxyvinyl trifluoromethyl ketones Sergey I. Vdovenko a, * , Igor I. Gerus a , Natalia V. Lutenko a , Valery P. Kukhar a , Jacek Wo ´ jcik b a Institute of Bioorganic Chemistry and Petrochemistry, National Academy of Sciences of Ukraine, ul. Murmanska 1, 02094, Kiev, Ukraine b Institute of Biochemistry and Biophysics, Polish Academy of Sciences, ul. Pawin ´ skiego 5a, PL 02-106 Warsaw, Poland Received 21 July 2006; received in revised form 7 November 2006; accepted 12 November 2006 Available online 20 December 2006 Abstract Spatial structure of six b-substituted enones, with common structure R 1 O–CR 2 @CH–COCF 3 , were R 1 =C 2 H 5 ,R 2 = H (ETBO); R 1 =R 2 = CH 3 (TMPO); R 1 =C 2 H 5 ,R 2 =C 6 H 5 (ETPO); R 1 =C 2 H 5 ,R 2 = 4- O 2 NC 6 H 4 (ETNO); R 1 =C 2 H 5 ,R 2 = C(CH 3 ) 3 (ETDO) were investigated by 1 H and 19 F NMR, infrared spectroscopy and AM1 calculations. NMR spectra revealed that enones (MBO), (ETBO) and (TMPO) are exclusively (3E) isomers, whereas in (ETPO), (ETNO) and especially in (ETDO) the percentage of (3Z) isomers is significant and depends on the nature of solvents. Conformational behaviour of studied enones are determined by the rotation around of C@C double bond, @C–C and @C–O single bonds (correspondingly trifluoroacetyl and alkoxy groups), and (EZZ) conformer being the most stable in all cases. IR spectra revealed that with the exception of (ETDO) (EZZ) conformer is most populated in all cases. Bulky substituents like phenyl or tert-butyl group at b-position of enone result in the equilibrium mainly between (EZZ) and (ZZZ) forms, whereas b-hydrogen and b-methyl substituents determine the equilibrium between (EZZ) and (EEZ) or (EZE) conformers. Ó 2006 Elsevier B.V. All rights reserved. Keywords: NMR and IR-spectra; Conformational analysis; Enones; AM1 calculations 1. Introduction Presence of rotational isomerism in b-substituted alkoxy- vinyl methyl ketones [1–3] prompted us to investigate spatial structure of b-substituted alkoxyvinyl 1,1,1-trifluo- romethyl ketones. Earlier [4–6] we investigated structure of a,b-unsaturated enaminoketones with trifluoromethyl group and showed these enaminoketones to possess differ- ent configurations as a result of hindered rotation around C@C double bond, @C–N single bond between amino- and vinyl moiety and @C–C single bond between vinyl and carbonyl group. b-Substituted alkoxyvinyl 1,1,1-tri- fluoromethyl ketones are precursors of corresponding flu- orocontaining enaminoketones, possessing another additional degree of freedom, viz ability of rotation around C–O single bond. Martins et al. [7–9] studying various 1,1,1- trihalomethyl a,b-unsaturated enaminoketones also point- ed to the existence of different rotational forms. From works of Dabrowski and Tencer [1,3] and Martins et al. [7,8] it is known b-substituent to insert additional constrains to hindered rotation around double C@C and single @C–C and C–O bonds in a,b-unsaturated enones thereby stabiliz- ing some stereoisomeric forms and disturbing others. Con- sequently the number of possible forms diminishes thus facilitating the interpretation of data obtained. Continuing studies of rotational isomerism in a,b-unsat- urated trifluoromethyl ketones we decided to investigate the influence of b-substituent on spatial structure of triflu- oromethylacetyl-a,b-enones. Hence, the aim of present work is to determine and evaluate percentage of specified spatial forms of b-substituted alkoxyvinyl trifluoromethyl ketones by the methods of 1 H and 19 F NMR, IR-spectros- copy and MO calculations, carried out by the Austin Model 1 (AM1) semi-empirical method. For comparison 0022-2860/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2006.11.032 * Corresponding author. Tel.: +380 44 573 25 93; fax: +380 44 573 25 52. E-mail address: sergiusz@bpci.kiev.ua (S.I. Vdovenko). www.elsevier.com/locate/molstruc Journal of Molecular Structure 840 (2007) 125–132